Impossible to know much without any system info and details about the project. Most 26 :: XX errors are genuine structural issues in the project like property streams not updating or referencing wrong plug-ins. More info will definitely be required to even come close to a guess on what's actually going on.
Instead of opening the project, could you try importing it into a fresh project? Also, what's the version of After Effects you're using: https://community.adobe.com/t5/after-effects/faq-how-to-find-the-exact-version-of-after-effects-you-...
Let us know if it helps.
Thank you for your suggestions, my friend just helped me resolve the problem.
So that you might help others, how did you and your friend resolve the problem, please?